Scalable and reconfigurable true time delay line based on an ultra-low-loss silica waveguide

A scalable and reconfigurable on-chip optical true time delay line consisting of Mach-Zehnder interferometer (MZI) switches and delay waveguides is proposed and demonstrated with the ultra-low-loss silica waveguide platform. The MZI switches provide the reconfiguration of the light traveling paths and hence different delays. Our proposed structure can be easily scaled to an M bit delay line with a slight increase in dimensions. The footprint of our fabricated 1 bit delay line is 33  mm×13  mm (length×width) and can provide a delay of 6.0 ps with an insertion loss of 1.2 dB at the operating wavelength of 1550 nm, while the footprint of the 4 bit delay line is 43  mm×14  mm and can provide a discrete delay tuning from 6.0 to 90.2 ps with a delay deviation lower than 0.2 ps and a tuning response time of 0.84 ms. The insertion losses are lower than ∼2.34  dB, and the extinction ratios are greater than 20.42 dB. The average switching power is ∼132.6  mW. Our proposed optical true time delay lines could find applications for optical beamforming in phased array antennas.